Phase and amplitude control circuit for electronic function generators



June l, 1948.

l M. L. GRI-:ENOUGH Filed sept. 28, 1945 2 Sheets-Sheet 1 adm/r! caf/wf June 1, 1948. M. L. GRI-:ENOUGH 2,442,597

PHASE AND AMPLITUDE CONTROL CIRCUIT FOR ELECTRONIC FUNCTION GENERTORS Filed sept. 28, 1945 2 sheets-smet 2 INV EN TOR.

Patented June v1, 1948 PHASE AND AMPLITUDE CONTROL CIRCUIT FOR ELECTRONIC FUNCTION GENERA- TORS Maurice Leighton Greenough, Groveland, Mass., assignor to Radio Corporation of America, a corporation of Delaware Application September 28, 1945, Serial No. 619,238

UNITED STATES PATENT OFFICE 6 Claims. (Cl. 178-44) tion circuit for a magnetic variocoupler arranged for controlling the phases and magnitudes of output voltages which are non-linear functions of an input voltage applied to said variocoupler.

In electronic computing systems for solving ballistic functions in the process of sighting a gun at a remote fixed or movable target, lit is customary to derive the present slant range data by means of optical or radar sighting apparatus. The slant range data thus obtained are in polar coordinates which often must be converted into the rectangular or Cartesian coordinates representing present elevation and present ground range. In the case where the slant range tracking data is derived by radar apparatus, the slant range may be represented by an alternating voltage having a magnitude corresponding to the value of the slant range.

The instant invention comprises a phase correction circuit for a precision variocoupler wherein the alternating voltage having a magnitude corresponding to the value of the slant range is applied to a stator winding to establish a magnetic field having an intensity corresponding to th value of the slant range. A pair of mutualh7 perpendicular rotor coils rotatable within the magnetic eld provide output voltages having magnitudes corresponding to the sine and cosine, respectively, of the field energizing voltages. The rotor output voltage having a magnitude corresponding tothe product of the sine of the angular rotation of the rotor and the magnitude of the stator energizing voltage is proportional to the value of the present elevation. The rotor output voltage corresponding to the product of the cosine of the angular rotation and the magnitude of the stator energizing voltage is proportional to the value of the present ground range.

Since ballistic functions must be solved with an extremely high degree of accuracy, it is essential that the derived sine and cosine function currents be extremely close approximations of the true sine and cosine function values, and that the phases of the derived currents bear predetermined relation to the phase of each other and the input current. It is also essential that current scale factors be precisely maintained.

Since mechanical and electrical limitations in the variocoupler inherently limit the accuracy with which such devices may be constructed, it is essential that auxiliary means must be included for correcting for distortion of the energizing magnetic eld due to shielding effects, etc., in order that null current values may be obtained from the rotor windings with precisely angular separation. Without such correction the null points may deviate from the 180 angular separation by several mils of angle even when great care is taken in construction and assembly of the variocoupler.

The invention contemplates the use of a variocoupler of the type described wherein the stator windings are designed to produce a substantially uniformly distributed magnetic eld. The stator support comprises a pair of hemispherical insulating members each having a plurality of separate series-connected winding sections supported in slots on the external surfaces of the sphere, the density of the stator windings being substantially constant along the axis of the coil. The rotor windings are each Wound in pairs of peripheral slots which are mutually perpendicular. In order to insure that the stator eld may be accurately proportional in magnitude to the value of the energizing voltage, a plurality of feedback windings are wound in other peripheral slots on the stator support intermediate the several stator Winding sections.

The method and means of employing the currents from the feedback winding to compensate for variations in the gain of the driving circuit and for the effects of resistance in the variocoupler windings is disclosed and claimed in the copending application of Arthur W. Vance, Serial No. 607,887, filed July 30, 1945, assigned to the same assignee as the instant application. In the device described in said copending application the stator is energized'by signals derived from an input amplifier or other circuit, not shown, which is responsive to the present slant range alternating signal voltage. The feedback winding is connected through a variable phase control and a variable 'amplitude control to the input circuit of the amplifier in a manner whereby the amplifier input voltage and the feedback voltage are in phase opposition, and wherein the amplitude of the feedback voltage is but slightly less than the amplitude of the input voltage. Thus the uX density generated by the stator winding is substantially determined by the magnitude of the input Voltage to the amplifier, and is almost independent of amplifier gain and the resistance of the field windings. The system thus described may be termed a constant flux feedback system wherein the output voltages derived from the rotor windings are substantially trigonometric functions of the input voltage magintudes, proclosed and claimed in applicantsicopending 11.58,'

application, Serial No. 619,239; filed September 28, 1945, which describes the use of separate angularly-adjustable, small correction coilswhichV are serially-connected with theirotorwindings:

and adjustably coupled to the stator field whereby the null current points in the rotor circuits may be adjusted to an angular separation of 'pre1 cisly 180 as the rotor windings are rotated.

The instant invention comprises a control circuit for each ofthevariocoupler rotort winding circuits vfoi'5corltlolllg thcphases and amplitudes ofthecurrents derivedfrom; each of the rotor windings.` The inductive reactance of veach rotor windingis neutralized by` an 'equal series capacitive reactance, thus: mondige an effectively resistive output termination 'impedance frorn-Y each rotor winding. The required phase shift for each rotor winding circuitis provided by a. variable, capacitor shuntedacross the resistive termination. [In-:1 order!I to prevent *harmonic accentuation, separate smallrresistors are' seriallyconnectedwitheach phase shifting capacitor. Adjustment vof `the variable capacitors provides the desired phase` shift.- Adjustment Uffa variable autoftransformer: Connected; t0 'the phase controlled. circuitprovides; output-:current ampli: tud@ COI1t1`01- ifi". t

One ofthe objects of. the invention is 'to provide an improvedi methodifof, and means. for electronically deriving i' nono-:linear :functions of a variable quantity. :Another iobject' of ,theginventionis tplprovide animproved' electronic function generator fon derivingitcurrents' having magnitudes whichzare'non-flinearffunctions of the magnitude of an applied current. and;which bear predetermined phase relation.- :to .said appllied current. further fobj ect. :of ;the invention is, ito providean improved electronic.;tracking device and phase correction. circuit forcconverting the values of--a variable-quantity in polar." coordie nates tocorresponding values of! said variablej in Cartesian -.'coordinates.V` AnA additional. objectsof the invention-2 isi to provide. animprovedi vari.- ocouple'rand output phase'and 'amplitudeadjusting circuitfor converting an energizing alternat-i ing! potential to -other potentials corresponding in magnitudes tothej sine arid-cosine ofithe magnitude ofthe-ener'gizing potentialwith respect to the angular Y.dis-placement of-` theA rotating element ofthe varioo'o'uplerr' i t Anotherpbject isi` tc '-p'rOvide an improved methodg-of and means foradjusting the' relative phases and amplitudesfof output currents 1 'de' rived from; a non-linear *function Vgenerator excited by-alternating currents. A further-object isto provide meansfor neutralizing-'the reactar-ice inthe output circuitof an `inductive non-line'ar function generatorfand AmeansVfor adjusting the relative Aphases and' amplitudesV -off a plurality of Vsai-dfneutralizedoutput circuits; 5

y The inventionv will.'jbe""described in'Y greater detailfby reference "to 'the accompanying draw-f ing of which. Figureli i is. a schematic", circuit diagram of a preferred embodiment thereof, FigL ure 2 is an elevational cross-sectional View taken along the lineY II-IL and Figure 3 is a side elevational view of a preferred embodiment of a variocoupler comprising an essential element of the network schematically shown in Figure l.

Similar `reference characters Aare applied to similar elements throughout the' drawing.

Referring to the circuit of Figure 1, input 'signals having a frequency, for example, of 2500 C. l?.Y Si., arel applied to the input terminals I,

- 3 which areiccnnecte'd to the stator winding 5 of a varicouplerlfofthe type generally described heretofore. The 'variocoupler 7 includes a pair cf'mutually'perpendiular rotor windings 9, Il,

4whichf aren 'continuously and simultaneously retatablewithin'the uniformly distributed mag- 1 neticeld produced by energization of the stator v'vindings;`= The rst rotor winding 9 is coupled through "a first amplitude and phase adjusting circuit i 3 to output terminals l5, I7, which providecurrents proportionalin magnitudeto' lthe sine ofthe magnitudes ofthe input current." The second rotor winding.,Y l i is 'coupled: through a second amplitude L and phase adjusting: circuit la tof otheroutput terminals 2 I 23,'fo'rcderiving currents of magnitude proportional'tothe cosine cf the magnitudeof'the input' signalfcurrents.

A feedback winding 251xedly supported with respectV to ,the vstator windings Sf geerat'es a' feedback current which i's-iutilizedi as described in said copending Vanceapplication?forinsert ing in s erie's withithe` input. voltage voltage in phase oppositionV to and* but: Tof.'V slightlylowei magnitude thanv said' inputvolta'ge HThe` nfag= nitude of the energizing.' 'field'. generated? by. the stator'winoling '5 thus is'substantiallydetermined by the magnitude `ofsaidinputFvoltag applied tothe inputiterrninalsl l an'd .3 and -issub'stantiallji independent. of variations "the gainrofffthe input circuiti and vof fthe-'rsistance ofthe-e'l'd and feedback variocoupler` 'windings '5" 'and Y25; It shouldl'be -understoodfthat the 'istre'ngtl" of the ie'edback: v:voltage be fcotrolred1- by the: number? of C turns onfthe'l feedbaclr. winding; and

that: :the ienergi z'ing`Y neld intensity 'audstabil itymayfbe cmitrllecl byffanadjustmentfofithe phase' andi amplitude off'lthe' feedback" current since itLis 'desirable-thatfthe output currents' derivee 'fromfthef output tenniiialsy 'l 5,41 tand! 21;

magnitudes tftne 'currents energizing-trigger@ windings, kit isessenuailtnatcapacitivecoupling nette'errl me' various windings of 'the yancoupler be I'entstandany eliminated since" such] capacitive coupling fwo'uie -prcveneuuouseutput"currents frornthe;v rotor windings andfwouldalfso permit A f rst variable?capacita 7 3 l and prevent high v current amplitudejcontrol' tapped;'autQFtTaIiSfQiie 35 .,e31S`..,. Il controlled resistive termination of the"-rotc'vrvvin'd put terminals 2|, 23 are connected, respectively,

to 'a movable tap 49 and to one terminal of said second transformer.

Referring to Figures 2 and 3, a preferred embodiment of an accurately aligned variocoupler comprising an essential component of the function generator circuit shown in Figure 1 includes a pair of substantially hemispherical stator insulating supports 53 and 55 which may be telescoped together at the joint 51. The external surface of the stator sections include peripheral slots for supporting a plurality of sections 5 of the stator winding 5. The stator sections 5 are wound with insulating conductors and are serially-connected yby means of jumpers 59 between adjacent winding sections. The numbers of turns on each 'coil section, and the spacing between adjacent coil sections, are arranged to provide a constant winding density along the axis 5| of the coil to produce an electromagnetic field having substantially uniform intensity. The seriallyconnected stator-winding sections 5 are terminated in a pair of input terminals 63, |55. The ends of the serially-connected stator winding 5 on each of the hemispherical stator supports 53, 55 are terminated in additional terminals 51, 69 which may be connected together by means of a jumper lead, not shown, after the variocoupler is assembled.

The feedback winding 25 comprises a plurality of small winding sections 25' which are similarly connected together by jumpers 1| on each of the stator supports. The feedback winding sections 25 each comprise relatively few turns supported in other peripheral slots disposed intermediate the stator winding sections 5. TheA output terminals 13, 15 of the feedback winding provide for connection to the feedback circuit, and the two halves of the feedback winding are terminated in terminals 11 and 19 which are connected together by means of a jumper lead, not shown, after the variocoupler is assembled. The internal surfaces of the stator supports 53 and 55 are coated by means of a conducting shield 8| which may be grounded in any well known manner. The conductive electrostatic shield 8| may comprise, for example a coating of carbonaceous material applied in fluid form and permitted to solidify.

The rotor windings are supported on a substantially spherical insulating support 85 which is rotatable with a rotor shaft 81 journalled in suitable bearings 89 mounted on the stator support. The rotor shaft 81 preferably is hollow in order that the rotor winding terminal leads may be conveniently brought out to conventional slip rings 9| and contacts 93 or other rotor terminals. The rotor support 85 includes a pair of perpendicularly disposed radial channels 95, 91 for the output terminal leads from the rotor windings. The hollow rotor shaft 81 includes suitable apertures 99 in the periphery thereof for permitting the rotor winding leads to be brought through the hollow shaft.

The rotor windings 9 and are' wound in mutually perpendicular pairs of peripheral slots in the rotor support 85, and terminated in suitable terminals set into shallow depressions ||l| in the rotor support. The rotor winding terminals are connected by means of pairs of iiexible insulating leads |03 and |95 which pass through the channels and 91 and through the center 'of the hollow rotor shaft 81, to the external terminating means. The individual rotor coil sections 9' and include individual electrostatic shields |01 which may comprise, for example, a thin layer of metallic foil surrounding each of the winding sections. The several rotor coil shields may -be connected together and grounded to the rotor shaft in any conventional manner. The stator and feedback windings and the rotor support including the slots for the perpendicularly disposed rotor windings should be as accurately aligned as possible. The rotor shaft 81 also should be accurately alignec i with one of the center axes of the stator in order that output currents derived from the rotor windings may substantially approximate true trigonometric functions of the energizing current applied to the stator winding.

A'Ihe stator supports 53, 55 preferably should v Thus the invention disclosed and claimed-herein comprises a circuit for controlling the phases and amplitudes of the currents derived from the normally-disposed rotor windings of a precision type variocoupler having its stator windings excited by alternating potentials. The phase and amplitude controls for each rotor winding operate substantially independently to provide accurately-phased sine and. cosine function currents having the desired scale factors.

I claim as my invention:

1. Apparatus for deriving currents having instantaneous amplitudes equal to a non-linear function of the instantaneous amplitudes of applied currents including means responsive to said applied currents for establishing a substantially uniform alternating magnetic field, inductive means selectively rotatable through a predetermined angle within said eld for deriving output currents having amplitudes approximately proportional to said function of said angle, capacitive means for resonating said inductive means to the frequency of said applied currents to provide a resistive termination for said output currents, a phase shifter connected to said resistive termination for adjusting the phase of said output currents and means for adjusting the magnitude of said output currents.

2. Apparatus for deriving currents having instantaneous amplitudes equal tc a non-linear function of the instantaneous amplitudes of applied currents including means responsive to said applied currents for establishing a substantially uniform alternating magnetic field, inductive means selectively rotatable through a predetermined angle within said field for deriving output currents having amplitudes proportiona1 to the density of Said field and approximately proportional to said function of said angle, a series capacitor for resonating said inductive means to the frequency of said applied currents to provide a resistive termination for said output currents,

y Y t 'say capacitive phaseshifter inrshunt with :'saidre- :Sistine termination for adjusting :the fphase Of saidnutput 'currents rand means fior :adjusting the magnitude: of said :phase adjusted iouput vvc1411'- lrents. Y s Y Y 3. Apparatus according to claim-52 including a Jresistor serially-connected with .saisi i'phase shifter :to prevent harmonicgaccentuation fdue :to seriesresonance of'said inductive means and'said `-phase shifter. Y il. 4Apparatus :for deriving .currents `hai/ingin- .fstantaneolls V ..tIIl-pl-itudes egual ,to a non-linear `function of thezinstantaneousamplitudes of applied-,currents including a riirst Winding having tconnections .for said applied Acurrents for 'esv tahlislflingV a :substantially uniform valternating magnetic eld, a second 4Winding selectively mtatable through a predetermined aug-le within said ffield for deriving output currents having vamplitudes proportional to the density 'of said field-and approximately proportional lto fthe .sine

y.of said angle, a lseriescapacitor for resonatlng said second winding to the frequency 0f said applied currents to provide a resistive terminationfor said output currents, -a resistive-capacitive phase shifter in shunt with said resistive :termination for adjusting :the phase of :said output vcurrents and voltage adjusting means for said phaseadiusted output currents. Y

5. Apparatus lfor. derivingy currents having -nstantaneous amplitudes equal to a non-linear functionxofY the instantaneous amplitudes of applied currents including .ga Vfirst winding having connect-ions for said applied currents -f0rV eS- QLD tude to saiddensity-of said held-and approximate- -lyproportional `.to the ,cosine of said `angle, series capacitorsforresonating each ofsaidsecondoand third windings to the frequency of ,said applied .currents to y provide resistive terminations ,for .said output currents, .a Vresistivecapacitive phase .shifter .in shun-t with each of said resistive ,terminations f-or adjusting the phases -of saidoutput .currents and volta-ge adjusting V.means for .each

of-said phase adjusted output currents. v

`6. Apparatus according to claim .fwhereinsfld lvolta-ge adjusting means comprises an adjustable transformer shunt connected /With said .phase shifter. I

LEIGHTQN GREENOUGH.

REFERENCES .CITED The Afollowing reflerencesare of record in the ileof thispatent:

SIATES PATENTS 

